In the operation of fossil fuel furnaces and power plants which burn oil, coal and/or natural gas, flue gases are discharged into the atmosphere as a by-product of furnace/plant operation. In addition to water vapour, carbon dioxide and nitrogen, flue gases typically contain as products of the fossil fuel consumption, other environmentally harmful substances such as nitrous oxides, sulphur oxides and, particularly in the case of coal-fired plants, fly ash and mercury.
Mercury (Hg) is a known health and ecological concern because it is a toxic, persistent, bioaccumulative substance. The major anthropogenic source of both elemental Hg0 and oxidized Hg arises from coal-based power generation. Once released into the environment, it converts in water to the highly toxic form of methylmercury, which accumulates in fish and other species. In recognition of the deleterious effects of mercury, various governments have proposed increasingly rigid emission standards mandating the capture of mercury from flue gas streams, to reduce the volume of mercury which is introduced into the environment. As a result, there has derived a need to better monitor flue gas mercury content, and in particular the elemental mercury content in coal-furnace flue gases to assess not only the level of mercury released thereby, but also the operating efficiencies of environmental controls and mercury capturing devices.
At present, most mercury level monitoring is performed by wet chemistry analysis using an extractive gas process. Such conventional wet chemistry methods are slow and expensive, involving highly trained staff and the physical removal of a sample volume of gas from the flue gas stream via a conduit pipe. The inventors have appreciated that in addition to difficulties in transferring gas samples for remote analysis, conventional methods suffer a further difficulty in that the physical transfer of the extracted gas sample, inherently provides a delayed response. As a result conventional mercury analysis systems are poorly suited for providing real-time measurement of coal-furnace emissions.